Genomic Analysis Of The Antarctic Psychrotrophic Bacterium Psychrobacter Sp. G And Expression Analysis Of Its Cold/heat Shock Protein Genes

Antarctica is a cold environment which experiences large sunlight andtemperature fluctuations, the specific geographic and climatic characteristics made it adistinctive ecosystem. Antarctic microorganisms have developed particular adaptationmechanisms that successfully enable them to thrive in this harsh environment.Genome sequencing and gene function annotation were performed to obtain genesinvolved in temperature adaption in the Antarctic bacterium Psychrobacter sp. G.qRT-PCR was performed to evaluate the expression characteristics of cold/heat shockprotein (CSP/HSP) genes under temperature/salanity stress, and the potentialinfluences of regulatory sequences on the expression were also analyzed. The study ishelpful to further clarify the adaptation mechanism of Psychrobacter sp. G.The optimal growth temperature and salinity of Psychrobacter sp. G was20and45respectively, suggesting that it was a psychrotrophic. Its genome was3087702bp in length,2721ORFs were predicted from it, and1891of them were annotated.Blast2GO program were used to perform the GO annotation. The results showed that81of the predicted ORFs were involved in stress response, such as CSP, HSP, DNArepair protein, and chaperone protein. Three CSPs (Csp1137, Csp2039, and Csp2531)and five HSPs (Hsp845, Hsp1721, Hsp2538, Hsp2666, and Hsp2667) were selectedand their full length sequences were cloned.Multiple sequence alignment and phylogenetic analysis showed that Csp1137,Csp2039, and Csp2531were highly conserved and homologous with CspA, andthey also had RNP1and RNP2motifs that are known to be involved in binding tosingle strand nucleic acids. qRT-PCR revealed that the expression of Csp1137was enhanced both by low (0,10) and high temperature (30). Theexpression of Csp2039was enhanced by low temperature (0), but was lowerthan that of Csp1137, which might be explained by the absence in Csp2039gene of the AT-rich UP element and cold box. The expression of Csp2531wasinhibited by low temperature (0), even with the presence of AT-rich UPelement, and it was also not sensitive to high temperature (30). The expressionof Csp1137was enhanced by high salinity (90,120), whereas that of Csp2531wasenhanced by low salinity (0,15). Both low (15) and high (90,120) salinityrepressed the expression of Csp2039. The expressions of the three CspAs wereaffected by environmental salinity, indicated that they may be involved in theadaption of the strain in response to salinity stress.Multiple sequence alignment and phylogenetic analysis showed that Hsp845,Hsp2538, Hsp2666, and Hsp2667were belonging to GrpE, Hsp15, GroES, andGroEL family, respectively; Hsp1721was assumed as HSP on the basis of thesimilarity analysis. qRT-PCR revealed that the expressions of the five HSP geneswere all enhanced immediately after exposed to high temperature (30). Whenexposed to30°C, the expression of Hsp845reached its maximum with a value of11.7-fold compared to control after2h treatment; although the relative expressionlevel of Hsp1721were much lower than that of the other four HSP genes, Hsp1721might be involved in the adaption of the strain in response to temperature stress.The expression of Hsp2666and Hsp2667were highly synchronized after exposure to30°C. The expression of Hsp1721, Hsp2538and Hsp2667were not affected bylow salinity (0,15) treatment, while the expression of Hsp845and Hsp2666wereenhanced under this condition. The expressions of the five HSP genes were allenhanced by high salinity (90,120) treatment. One explanation was that thechange of environmental osmotic resulted in the accumulation of the denaturedprotein, and then enhanced the expression of HSP.The study provided basic materials for the clarification of the adaptationmechanism of the Antarctic psychrotrophic bacterium Psychrobacter sp. G andthe role of the cold/heat shock proteins playing in its adaption to Antarcticenvironment.